export default function loginBgAnimation() {
    const windowWidth =
        document.documentElement.clientWidth || document.body.clientWidth;
    const windowHeight =
        document.documentElement.clientHeight || document.body.clientHeight;
    let count = 0;
    const canvas = document.getElementById("bg-canvas") as HTMLCanvasElement,
        ctx = canvas.getContext("2d") as CanvasRenderingContext2D,
        w = (canvas.width = windowWidth),
        h = (canvas.height = windowHeight),
        hue = 217,
        stars: IntStart[] = [],
        maxStars = 1500; //星星数量

    const canvas2 = document.createElement("canvas"),
        ctx2 = canvas2.getContext("2d") as CanvasRenderingContext2D;
    canvas2.width = 100;
    canvas2.height = 100;
    const half = canvas2.width / 2,
        gradient2 = ctx2.createRadialGradient(half, half, 0, half, half, half);
    gradient2.addColorStop(0.025, "#CCC");
    gradient2.addColorStop(0.1, "hsl(" + hue + ", 61%, 33%)");
    gradient2.addColorStop(0.25, "hsl(" + hue + ", 64%, 6%)");
    gradient2.addColorStop(1, "transparent");

    ctx2.fillStyle = gradient2;
    ctx2.beginPath();
    ctx2.arc(half, half, half, 0, Math.PI * 2);
    ctx2.fill();

    // End cache

    function random(min: number, max = 0) {
        if (arguments.length < 2) {
            max = min;
            min = 0;
        }

        if (min > max) {
            const hold = max;
            max = min;
            min = hold;
        }

        return Math.floor(Math.random() * (max - min + 1)) + min;
    }

    function maxOrbit(x: number, y: number) {
        const max = Math.max(x, y),
            diameter = Math.round(Math.sqrt(max * max + max * max));
        return diameter / 2;
        //星星移动范围，值越大范围越小，
    }
    interface IntStart {
        orbitRadius: number;
        radius: number;
        orbitX: number;
        orbitY: number;
        timePassed: number;
        speed: number;
        alpha: number;
        draw: () => void;
    }
    const Star = function (this: IntStart) {
        this.orbitRadius = random(maxOrbit(w, h));
        this.radius = random(60, this.orbitRadius) / 18;
        //星星大小
        this.orbitX = w / 2;
        this.orbitY = h / 2;
        this.timePassed = random(0, maxStars);
        this.speed = random(this.orbitRadius) / 500000;
        //星星移动速度
        this.alpha = random(2, 10) / 10;

        count++;
        stars[count] = this;
    };

    Star.prototype.draw = function () {
        const x = Math.sin(this.timePassed) * this.orbitRadius + this.orbitX,
            y = Math.cos(this.timePassed) * this.orbitRadius + this.orbitY,
            twinkle = random(10);

        if (twinkle === 1 && this.alpha > 0) {
            this.alpha -= 0.05;
        } else if (twinkle === 2 && this.alpha < 1) {
            this.alpha += 0.05;
        }

        ctx.globalAlpha = this.alpha;
        ctx.drawImage(
            canvas2,
            x - this.radius / 2,
            y - this.radius / 2,
            this.radius,
            this.radius,
        );
        this.timePassed += this.speed;
    };

    for (let i = 0; i < maxStars; i++) {
        new Star.prototype.constructor();
    }

    function animation() {
        ctx.globalCompositeOperation = "source-over";
        ctx.globalAlpha = 0.5; //尾巴
        ctx.fillStyle = "hsla(" + hue + ", 64%, 6%, 2)";
        ctx.fillRect(0, 0, w, h);

        ctx.globalCompositeOperation = "lighter";
        for (let i = 1, l = stars.length; i < l; i++) {
            stars[i].draw();
        }

        window.requestAnimationFrame(animation);
    }

    animation();
}